This invention relates to molded bodies or shaped articles which contain metals and/or metal compounds as inclusions in very finely divided form. The invention is also directed to a process for the production of these molded bodies having such inclusions.
The inclusion or embedding of relatively inert compounds into molded polymer articles has been known for a long time. In general, additives such as pigments or the like are incorporated into the polymer during its initial formation or in a premolding mixing and extrusion procedure. The best known process of this type is the spin-dyeing or delustering of polymer filaments and films. For this purpose, there are used a number of pigments readily available on the market, such as titanium dioxide, aluminum oxide, aluminum silicate, zinc sulfide, etc.
The particle size of these additives lies on the order of a few microns (.mu.). If a smaller size is required, it is necessary to subject the particulate mass to a comminution process, for example, by milling for a relatively long time in a bead mill or a similar grinding or pulverizing means. In general, particle sizes are reduced in this manner to approximately one .mu..
For a particular purpose, namely for catalytic membranes, another process for the incorporation of certain compounds into the membrane has become known. Thus, permeable membranes are described in U.S. Pat. Nos. 3,846,236 and 3,996,141 which contain a catalyst for the decomposition of hydrogen peroxide into water and molecular oxygen. Such membranes are especially suitable for use in artificial lungs.
As is also known from the cited state of the art, suitable membranes are those made of water-insoluble, water-wettable cellulose derivatives such as cellophane (cellulose regenerated according to the viscose process), cellulose ester, carboxymethyl cellulose and also insolubilized gelatin or partly hydrolyzed polyvinyl acetate. Suitable catalysts to be incorporated in the membrane include manganese dioxide, ruthenium oxide or sulfide, and silver, gold or platinum particles.
For the production of catalyst membranes which contain ruthenium oxide, one process is described in U.S. Pat. No. 3,996,141, wherein the membrane is treated simultaneously on one side with a metal salt solution, e.g. with a ruthenium chloride solution and on the other side with an alkali hydroxide solution. In this manner, a shaped or molded body is obtained in which there has been incorporated or embedded a metal oxide and especially ruthenium oxide.
A number of difficulties have become apparent when working according to the known process. In particular, the known process does not permit a continuous production of these types of membranes. Thus, the incorporation of the oxide into the membrane does not proceed quickly enough due to the relatively slow diffusion of the liquid into the solid body. The corresponding long residence time of the membrane in the aqueous NaOH solution has a bad influence on the mechanical properties of the membrane, in particular causing a reduction in its strength. Furthermore, in order to avoid troublesome oxide precipitations in the metal salt bath, any mixing of the metal salt solution with the alkali hydroxide must be prevented. This is especially difficult in carrying out a continuous process, since the membranes used here as sealing surfaces or separating means must also be moved through the bath.
With a sequential arrangement of the treatment baths, problems arise through the carrying off of metal salt solution from the first bath into the following alkali bath, especially with reference to maintaining a clean and carefully supervised process. On account of the permanent alkali depletion in the precipitation bath in a continuous process, it is difficult to maintain over extended periods of time those constant precipitation conditions which are necessary to achieve a homogeneous inclusion of the metal oxide.
In general, the processes known in the prior art do not lead to satisfactory results, especially under continuous operation, and the final products have a poor distribution of the fine particles, lacking any uniform pattern of distribution. Moreover, the mechanical strength or stability of the resulting catalytic membrane is often insufficient to prevent a tearing or breaking open of the membrane when placed in actual use.